Call-distributing system



S. B. WILLIAMS, In.

CALL DISTRIBUTING SYSTEM. I APPLICATION man NOV- 28. 1919.

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Patented Oct. 11, 1921.

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APPLICATION FILED NOV. 28, I919- Patented Oct. 11, 1921.

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CALL DISTRIBUTING SYSTEM.

APPLICATION FILED NOV-28, 1919.

1,393,727; Patented Oct. 11, 1921.

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UNITED STATES PATENT OFFICE.

SAMUEL B. WILLIAMS, JR., OF BROOKLYN, NEW YORK, ASSIGNOR TO WmTERN ELEG- TRIC COMPANY, INCORPORATED, OF NEW YORK.

YORK, N. Y., A CORPORATION OF NEW CALL-DISTRIBUTING- SYSTEM.

Application filed. November 28, 1919.

To all whom it may concern:

Be it known that I, SAMUEL B. WILLIAMS, J r.,a citizen of the United States,residing at Brooklyn, in the county of Kings, State of New York, have invented certain new and useful Improvements in Call-Distributin Systems, of which the following is a tul, clear, concise, and exact description.

This invention relates to telephone exchange systems, and more particularly to systems of the type employing automatic switches for distributing calls to the connecting circuits of operators positions.

The object of the invention is to provide equipment at a manual exchangeby means of which a calling line may be extended with a minimum of delay to an operators position, and by means of which a plurality of calls may be simultaneously initiated in the same group of subscribers lines without interference.

Heretofore in call distributing systems employing power driven switches of the panel type, such for example as disclosed in the patent to S. B. lVilliams, J r., Serial No. 1,30%,6 l1, issued May 27, 1919, the lines terminating in the exchange have been divided into groups of 500 lines each, each group being served by a plurality of line finders. Each line finder is equipped with ten brush sets arranged to hunt over the ten banks to which the lines of the group are connected. Thus, each group of lines is subdivided into groups of 50 lines each, each subgroup having individual thereto a so-called group an cuit. Common to ten of these group circuits is a starting circuit which is arranged to cause one of the finders which has been preselected by the advanced starter wire circuit to start, the particular brush set which is tripped being dependent upon the group circuit serving the group in which the calling line is situated. The group circuit is so coordinated that only one finder may be started upon the initiation of a single call,

other calls in the same group of 500 linesbeing delayed for a predetermined interval of approximately two seconds. In order to provide for continuous service, an elaborate arrangement of alarm lamps, signals, keys and relays has been necessary.

This invention is especially directedtoward the provision of improved circuits by Specification of Letters Patent.

Patented Oct. 11, 1921.

Serial No. 341,167.

means of which the calling lines of a group are first connected through quick-acting switches of small capacity to an operator selecting circuit, and subsequently connected directly to an idle cord of the selected operators position by relativelyslow operating swltches of large capacity. The nature of the calling line and the class of service to which the line is entitled is made evident to theoperator by means of a class of service ndicator assigned to the operators position, mmediately upon the extension of the calllng line to the position, and the further extension of the line is made by means of the selected cord circuit in accordance with such lndlcation and in accordance with instructions received from the calling subscriber. Upon the establishment of a connection to an idle cord circuit by the slow operating switches the quick-acting switches employed in the preliminary connection revert to commen use. i

It is the purpose of this invention to eliminate the use of group circuits and the attendant equipment by providing quick-acting line finders in the place of each group circuit, thus effecting a saving in the cost of equipment and a considerable saving of time for completing the connection. By the pro vision of means for effecting a quick connection with an operators position, it is not necessary to provide main line finders which operate quickly, and consequently finders having a smaller number of brush sets for cooperation with large subgroups of lines may be employed with a further saving in cost of equipment.

One feature of this invention is the provision of quick-acting line finders each having access to a relatively small group of the lines of the main group, and slow-acting line finders each having access to lines of the entire group.

Another feature of this invention is the provision of means for extending the calling line temporarily to an idle operators position and for warning the operator of a call incoming over some cord of the position.

Another feature resides in the provision of an allotting mechanism to govern the precedence of extension of calling lines to cords of the operators position.

A still further feature resides in the provision of mechanism at the operators position "for indicating the nature of the calling line and the class of service to which it is entitled.

Other :teat'iires relate to the general organization of equipment at a manual eX- change, the grouping of the various units, and the detailed construction of the various parts involved in these units, which will be set forth in the following description of the preferred embodimentof the invention.

It will be obvious to those skilledin the art that this invention is not limited to the particular type of equipment disclosed, but is applicable to systems employing other well-known switching and indicating de- Vices.

The invention is illustrated in the accompanying diagrammatic drawings in which;

Figure 1 shows one line of a main group of subscribers lines, a line finder switch for making a connection therewith, an operators cord circuit selector switch for extending a connection from the line to a cord circuit and linked to the line finder switch, together with the associated circuits and apparatus through the medium of which the switches are controlled.

Fig. 2 shows a portion of an operators cord circuit, and the necessary apparatus for charging calls, ringing-back on party line calls, and -listening-1n and out on established connections; I

Fig. 3 shows the calling end of the operators cord circuit, together with class of service signal lamps, and the circuit and apparatusthrough the medium of which the functions of the cord circuit are sequentially controlled.

Fig. 1 shows a primary line finder switch for making a preliminary connection with subscribers lines of a subgroup together with the associated circuits for controlling it, the wipers and starting relay of a similar finder being indicated by the dotted inclosure;

Fig. 5 shows a secondary line finder switch for making connection with lines extended through the circuits of primary line finders, an operators position finding switch for further extending a call to an idle operators position, a finder selector for selecting paired line finder and cord selector switches, together with the associated circuits and apparatus through the medium of which the switches are controlled; and

Fig. 6 shows the circuits common to an operators position for selectively controlling the class of service signal lamps.

The figures taken together with Fig. 2 at the right of Fig. 1, Fig. 3 at the right of Fig. 2 and Figs. 4C, 5, and 6 placed beneath Figs. 1, 2, and, 3, respectively, illustrate as much of a complete organization as is necessary to impart an understanding of the construction and mode of operation of the system.

General Description of Apparatus.

A single telephone line of a main group of 500 lines is shown in Fig. 1, it being understood that there are as many groups as are necessary to accommodate the lines terminating in the exchange. The main groups of lines are preferably divided into ten minor subgroups of 50 lines each, each subgroup being served by groups of primary line finders having a capacity of 50 lines each, and are also divided into five major subgroups of 100 lines each, each subgroup of 100 lines being served by one of the brush sets of each main line finder having access thereto. It would, of course be possible to slightly in crease the rapidity of line selection by re ducing the capacity of the primary line finders to 30 lines each, whereby the main groups of lines would be reduced to 450 lines each divided into 15 minor subgroups accessible to 15 groups of primary finders and divided into five major subgroups of 90 lines each served by five brush sets on the main line finders, but this reduces the ca-' pacity of the main line finders to 450 lines necessitating both a greater number o1 primary and main line finders. The line has associated with it at the central office a line relay 8, a cut-off relay 9 and, if it is amessage register line, a message register (not shown). Each line is also provided with one or more spring jacks 10 by means of which connection may be made with the line when a connection is extended thereto. The line represented as a calling line in Fig. 1 and the line shown as a called line in Fig. 3 may be lines of the same character similarly equipped and located at the same exchange; or the lines may be located at different offices. In the present instance the line shown in Fig. 3 is not illustrated with line finder bank terminals or with equipment for controlling line finders. The line A, shown in Fig. 1, is illustrated as provided with multiple terminals in the banks of main line finders LF and of primary line finders PLF, and with a starting circuit leading to primary line finder starting-relays oi' all primary line finders having access to the subgroup of lines in which the line A is located, the starting relays being com- -mon to the subgroup of lines.

The groups oflines have access to differentoperators positions and the circuits and apparatus common to each such position through the medium of primary line finders PLF, secondary line finders SLF and operators position finders OPF, shown in Figs. 1 and 5. In the particular system illustrated, it is assumed that there are 30 operators cords each accessible for extending a call. The operators cords being grouped into two positions of 15 cords each, although, if desired, the operators cords could be divided into 1, 2, 8 or more groups. The switches PLF, SLF, and OPF are all of the well-known step-by-step type in which a stepping pawl operates a ratchet wheel to which are connected brushes or wipers adapted to travel over the contacts of an arcuate terminal bank. These brushes or wipers are so arranged that for each step of the operating magnet the brushes or wipers engage a corresponding set of terminals. The primary finder switches and the operators position finders are each provided with six wipers and the secondary finder switches are each provided with five wipers. These switches have no normal position but stop in whatever position they are placed by their respective operating magnets.

The main line finders LF and cord selectors CS are not novel in themselves and have therefore been shown merely diagrammatically. These switches are substantially like the switch illustrated and described in the patent to J. L. McQuarrie, No. 1,177,0441, issued March 28, 1916. The line finder and cord selector are alike in all essential respects. Each comprises a longitudinally movable shaft 1 carrying as many sets of brushes 2 as there are groups of stationary terminals to be engaged. To move the shaft up, a depending extension of the shaft is brought into engagement with the constantly rotating power roller 3 by means of an idler wheel operated by the updrive magnet; and

'to move the shaft down the extension is brought into engagement with the power roller 4 by means of an idler wheel operated by the downclrive magnet.

Normally the brushes of each of the sets 2 are held apart so as to clear the associated terminals by means of a separating cam (not shown) located between the innermost brushes of the set. The brushes are tripped or released by means of trip magnets, such as 115. Each of these trip magnets when energized rotates an associated trip rod 5 that extends transversely to the switch shafts 1, and carries as many trip fingers 6 as there are finder switches in the group. The trip rod in rotating brings all of its trip fingers 6 into position to operate the brush controlling cams of the corresponding sets of brushes on all of the switches so that whichever of the finder switches is caused to move up has that set of brushes tripped that corresponds with the particular magnet that is at the time energized. When the finder switch that has been in use is returned to its normal position, any one of the associated controlling cams that has been tripped is engaged and rotated in a reverse direction to separate its switch brushes again and thus render them inactive.

Each of the line finder and cord selector switches has associated with it a commutator 7 which comprises a number of stationary commutator segments and a set of movable wipers carried at the top of the switch shaft 1 and cooperating with the stationary segments. This commutator serves to make and break a number of controlling circuits in the various stages of the movement of the switch shaft.

The finder selector FS, shown in Fig. 5, is also of the power-driven type and substantially like the switch shown in the patent to McQuarrie, hereinbefore referred to, but since only a single set of brushes is re quired, the brush selecting or tripping mechanism is omitted.

For controlling the circuit-s of the system there are employed a. number of sequence switches which are shown at different points and are designated 100, 300 and 500 respectively. These sequence switches may be of the type disclosed in the patent to Reynolds and Baldwin, No. 1,127,808, issued February 9, 1915. Each consists of an electro-magnetically controlled motor or driving mechanism and a number of associated switch springs. The switch springs associated with the sequence switch 100 are designated 101 to 113 inclusive. Those associated with the sequence switch 300 are designated 301 to 311 inclusive; and those associated with sequence switch 500 are designated 501 to 521 inclusive. To each of the contacts associated with the varioussequence switch cams are applied certain numerals. These numerals in the case of the springs 101, 301 and 501 indicate the only positions of the associated sequence switch in which these particular contacts are open; the numerals applied to all of the other contacts of each sequence switch indicate the only position of the particular associated switch in which the associate contacts are closed.

In Fig. 5, two allotter switches FA and SA are shown for determining the order of precedence of the selection of main line finder switches and the order of precedence of the operation of cord selector switches. These allotter switches are step-by-step switches of the well-known type each being provided with a single brush or wiper and a single row of bank contacts. The wiper of each allotter is adapted to be moved over its row of contacts by a stepping magnet which moves the wiper one step at each energization.

The identification of the lines with re spect to the class of service each is entitled to, is effected by means of an interrupting device. This interrupting device, as shown in Fig. 4, may consist. of a number of separate commutator disks assembled on the same shaft in a definite relation to each other and constantly rotated by means of suitable power mechanism. Brushes bear upon the commutator disks and serve to complete electrical connection between the disks and the external connections. Disks 415, 418 and 419 are constantly connected to battery through the disk 420. The disks 413 and 417 are connected to ground through the medium of disk 414. The disks 415, 418 and 419 have various and different combinations of conducting and insulating segments,

the arrangement being such that the circuit in which each of these commutator disks is included is made and broken in a way that is different from that in which each of the other disks makes and breaks its circuit. commutator disk 419 interrupts its circuit once per revolution, disk 418 interrupts its circuit twice and disk 415 interrupts its circuit three times.

The disks 413 and 417 serve to produce the pick-up impulses, which impulses cooperate with the identifying impulses produced by disks 415, 418 and 419 in a manner hereinafter explained to control the op- ;eration of the identifying mechanism-associated with each operators position. In order to simplify the drawing, the conductors leading from the brushes which engage the commutator disks413 and 417, to the registering relay mechanism in Fig. 6 have not been shown, but the ends of these conductors have been designated in both Figs. 4 and 6 by the letters a and b.

' line; The line relay 8 is energized, and in closing its contact establishes a starting circuit for the group of primary line finders which has access to the subgroup in which the line A is located. This circuit may be traced from ground at the armature of line relay 8, through the front contact of the armature, through the starting relays 400 of all idle primary line finders of the group, and through the common pilot alarm relay 401 to grounded battery. All idleprimary finders PLF of the group are thereby started up to hunt for the terminals of the calling line.

The start relay-400 of the finder PLF energizes over this starting circuit and at its left-hand armature closes a circuit for the stepping magnet 402, extending from the.

grounded pole of the battery through the winding and self-lnterruptlng armature conground.

tacts of the magnet 402, through the lefthand armature and front contact of start relay 400, through the back contact and outer right-hand armature of test relay 403, through the test wiper 404 and the bank contact upon which it is resting at the time the switch started, and assuming that the multiple terminals upon which the switch is standing are the terminals of another noncalling or busy line of the group, thence to ground atvthe back contact and grounded armature of the line relay of such line. At

its outer right-hand armature and front contact relay 400 closes a circuit for relay 405 which is energized. The stepping magnet energizes, stepping the finder switch one step to position its wipers upon the next set of bank terminals and interrupts its own circuit. This operation of the stepping magnet continues until the test wiper 404 engages the test terminal of the calling line from which ground has been removed at the back contact and armature of the energized line relay 8. Assuming that theswitch PLF is the first of the group to reach the terminals of the calling line, the test relay 403, which is connected in a branch of the circuit of the stepping magnet 402 extending to ground at the front contact and armature of slow relay 405, but which was shunted by ground encountered at the test terminals of non-calling lines, now energizes. Although the test relay 403 is now energized in series with magnet 402, the magnet 402 does not energize because of the resistance of relay Test relay 403 upon energizing opensat its outer right-hand armature and back contact, the circuit of ,the stepping magnet 402 and closes a circuit through this armature and its grounded front contact for placing a busy potential on the multiple test terminals appearing before the finder switches which have access to the calling line. At its inner right hand armature and front contact, relay 403 closes a circuit from grounded battery through resistance 406, over the, wiper 407 and bank terminal upon which it is resting and through the winding "of the cut-off relay 9 of the calling line to The cut-off relay energizes over this circuit and at its armature contacts opensthe circuit of the line relay 8 which thereupon deenergizes, restoring at its armature and back contact the non-calling or busy ground potential to the test terminals of the primary line finders, and opens at its front contact the starting circuits for all switches of the group. All started switches thereupon come to rest. The potential connected through the winding of the cut-off relay by the energization of relay 403, further serves to place a calling potential upon the test terminals of the calling line appearing at the banks of the line finders LF.

At its left-hand armatures and front contacts, relay 403 closes a circuit for the relay 408 which extends from grounded battery through the right-hand winding of relay 408, through the inner right-hand armature and back contact of relay 409, to the inner left-hand armature and front contact of relay 403, over the wiper 410 and bank terminal upon which it is resting, over the subscribers line loop, back through the upper bank terminal and wiper 411, through the outer left-hand armature and front contact of relay 403, through the outer right-hand armature and back contact of relay 409, and thence to ground through the left-hand winding of relay 408. Relay 408 upon energizing over this circuit opens at its armature and back contact the initial starting circuit through the relay 400 and closes therefor a holding circuit extending from grounded battery through the pilot alarm relay 401, through the winding of relay 400, and thence to ground through the armature and front contact of relay 408.

- Relay 400 upon energizing also removed ground potential at its outer right-hand armature and back contact, from the test conductor leading into the terminal bank of the secondary line switches SLF having access thereto, and closes at its inner right-hand armature and front contact a starting circuit for the secondary switch SLF, which extends frorn grounded battery through the start relay 522, through the lower contact of sequence switch spring 502 (1 and 2), and thence to ground at the inner right-hand armature and front contact of relay 400. Relay 522 energizes over this circuit and at its lower-most armature and front contact closes a circuit for the stepping magnet 523 of the secondary line finder which extends from grounded battery through the winding and interrupter contacts of magnet 523, through the lower-most armature and front contact of relay 522, through the lower contact of sequence switch spring 503 (1 and 2) through the back contact and right-hand armature of test relay 524, through the lower contact of sequence switch spring 504 (1 and 2), over test wiper 525 and the test terminal upon which it is resting, and if the bank terminals upon which the wipers of the switch are then resting lead to a primary line finder which has not been moved into connection with the calling line, thence to ground at the back contact and right-hand armature of relay 400 of such primary finder switch. The stepping magnet 523 upon energizing over this circuit moves the wipers of the secondary line switch SLF one step to the next set of bank terminals and opens its own circuit at its interrupter contacts. The stepping magnet continues to move the switch wipers over the terminal bank until the test wiper encounters the test terminal of the connection circuit leading to the primary switch taken for use, when no ground potential is found on the test termi nal. At this moment test relay 524, which has up to this time been held shunted by the ground encountered at the test terminals of the bank, becomes energized over a circuit extending from battery through the winding and interrupter contacts of the stepping magnet 523, through the winding of the test relay 524, through the lower contacts of sequence switch spring 505 (1 and 2), and thence to ground at the lower intermediate armature and front contact of start relay 522. The resistance of test relay 524 is such that the stepping magnet 523 does not energize in series therewith.

Test relay 524 upon energizing places a busy ground potentialon the test terminal of the set of bank terminals ofswitch SLF, upon which the wipers have come to rest over a circuit extending from ground at the lower contacts of sequence switch spring 506 (1 and 2), front contact and right-hand armature of relay 524, lower contact of sequence switch spring 504 (1 and 2), through wiper 525, and thence to the test terminal. At its left-hand armature and front contact, relay 524 closes a circuit to move the sequence switch 500 from position 1 to position 2, extending from grounded battery through the magnet winding of sequence switch 500, lower left-hand contact of sequence switch spring 507 (1), and thence to ground at the armature and front contact of relay 524. Under the control of its, master contact 501, the sequence switch moves out of position 1 and is brought to rest in position 2.

In position 2 ofthe sequence switch a circuit is closed from ground at the upper right-hand contact of sequence switch spring 508 (2 to 12), to the test wiper 525 to place a. busy potential on the test terminal of the bank upon which the wipers of the switch SLF are resting, which is maintained through the twelfth position of the sequence switch and replaces the busy potential placed thereon upon the energization of relay 524, and which potential is removed as soon as the sequence switch moves out of position 2. In the second position of the sequence switch a cir uit is also closed which may be traced from grounded battery through the winding of relay 409, through a bank terminal of switch SLF and wiper 526' resting thereon, and thence to ground through the lower left-hand contact of sequence switch spring 508 (2 to 12). Relay 409 upon energizing opens the circuit of relay 408 at its right-hand armatures and back contacts, thereby causing the deenergization of relays 400 and 405, and establishes at its left-hand armature and front contact a new holding ground for test relay 403 of the primary line finder to-replace the holding circuit heretofore maintained through the armature and front contact of relay 405. This circuit may be traced from grounded battery through the winding, and interrupter contacts of stepping magnet 402, through the winding of test relay 403, through the front contact and left-hand armature of relay 409, through the wiper 526 of switch SLF, and thence to ground at the lower left-hand contact of sequence switch spring 508. At the upper grounded contact of sequence switch spring 502 a holding circuit is established for the start relay 522 which is maintained through position 9 of sequence switch 500.

" Upon the initial energization of start relay 522, a circuit was also closed for the stepping magnet 527 of the operators position finder switch OPF, extending from grounded battery through the winding and interrupter contacts of stepping 1 magnet 527, through the upper intermediate armature and .frontcontact of start relay 522, through the back contact and inner armature of test relay 528 through the lower right-hand contact of sequence switch spring 509 (1 to 16), through the test wiper 529 and test terminal of the set of bank terminals upon-which the wipers of switch OPF are standing,,and if the operators position to which the set of terminals leads is busy, to ground at the armature and front contact of relay 200 (see Fig. 2),or to ground at the lefthand armature and front contact of relay 600 (see Fig. 6). The stepping magnet 527 energizesover this circuit and advances the wipers of the switch OPF onestep to the next set of bank contacts and interrupts its own circuit. If

the next operators position is busy, the switch advances another step and thus continues to advance step-by-step until an idle operators position is encountered, when no groundpotential will be found to exist on the test terminal of the bank ofthe switch. Assuming that the operators position, shown in Figs. 2 and 3, is the first idle position 7 tested for by the switch OFF, the stepping magnet will remain deenergized when the test wiper 529 encounters the test. terminal assigned to such position. Test relay 528, which has been shunted during the advance of the switch wipers over the terminals of busy operators positions by the ground potential at the test terminals of the bank, now energizes over a circuit extending from grounded battery, through the winding and interrupter contacts 30f stepping magnet 527, through the winding of test relay 528, and thence to ground through the front contact andupperarmaturefof relay 522. Stepping magnet 527 does not energize, however, in this circuit owing to the high resistance of test relay 528. Relay 528 upon energizing opens at its inner armature and back contact, the initial energizing circuit through the stepping magnet 527 at its inner armature and front contact extends a busy ground potential from the upper armature and front contact of relay 522 to'the test terminal of the set of bank terminals upon which the switch wipers have been brought to rest to prevent the seizure of the same operators position by a second finder switch, and at its outer armature and front contact closes a circuit for moving the sequence switch 500 out of position 2 and into position 3. This latter circuit may be traced from grounded battery through the magnet winding of sequence switch, and through the winding of left-hand contact of sequence switch spring 510 (position 2).

Warning tone to selected'opemtor.

In, position 3 of the sequence switch a circuit is closed for giving the operator at the position selected a warning tone, which circuit may be traced from the secondary of the warning tone transformer 530, through the upper left-hand contact of sequence switch spring 511- (3 to 11), over the lower heavy talking conductor, through wiper 531, and the bank contact upon which it is resting, and thence to ground through the upper right-hand winding of the operators repeating coil 201. The tone current flowing in this circuit produces by induction a tone current through the operators receiver 202. The operator upon hearing this tone is warned of the fact that a'call is about to be extended to one'of thecord circuits of her position.

In position 3 a circuit is also established for the relay 532 for a purpose to be described hereinafter, this circuit extending from grounded battery through the winding of relay 532,'through a bank terminal and switch wiper 533 resting thereon, and I thence to ground at the upper left-hand contact of sequence switch spring .512 (3 and 4E).

Selection of idle pair of Zine finder and 00rd selector switches.

A circuit is now closed for the relay 534 which initiates the hunting movement of the finder selector switch FS' which may be traced from grounded battery through the right-hand winding of relay 534:, through i the lower right-hand contact of sequence switch spring 513 (3 to 9), and thence to ground at the lower left-hand contact of sequence switch springs 513 Relay 53% spring 514 (3), and thence to ground at the front contact and right-hand armature of relay 534. As soon as the sequence switch moves out of position 3, the initial energizing circuit of relay 534 is opened, but upon its energization relay 534 has closed a circuit through its left-hand winding from grounded battery through the resistance 535, through its left-hand winding, through its left-hand armature and front contact, through the lower left-hand contact of sequence switch spring 515 (3 to 5), through the test brush 536 and the test terminal of the set of bank terminals upon which the finder selector brushes normally rest, and assuming that the paired line finder and cord selector switches accessible through this set of bank terminals is busy at this time, to ground at the lower right-hand contact of sequence switch spring 102 (2 to 18). Relay 534 at its right-hand armature and front contact also closed a circuit for the updrive magnet 537 of the switch FS which extends from grounded battery through the winding of the updrive magnet 537, through the upper left-hand contact of sequence switch spring 514 (4),, and thence to ground at the front contact and right-hand armature of relay 534. The updrive magnet upon energizing presses a depending extension of the switch shaft 1 against the constantly rotating updrive roller 3, thereby causing the switch shaft and brush set 2 to be moved upwardly over its bank of contacts. When the brushes of the switch engage a set of bank terminals corresponding to an idle pair of line finder and cord selector switches LF and CS, no ground potential is encountered by the brush 5336 upon the test terminal of such set of bank terminals, since the se quence switch 100 of the idle pair of line finder and cord selector switches is resting in position 1 and sequence switch spring 102 is opened at its lower right-hand contact, and, therefore, the holding circuit through the left-hand winding of test relay 534 is no longer complete. The relay 534 is, however, maintained energized until the switch brushes are properly centered on the selected set of bank terminals, bya circuit extending through the left-hand winding of relay 534, through the upper right-hand contact of sequence switch 515 (3 and 4) and thence to ground through the conducting portion 538 of the switch commutator 7, and shaft wiper 539. As soon as the switch brushes become properly centered upon the bank contacts, the shaft wiper 539 engages an insulating portion of the commutator and the relay 534 deenergizes.

Certain of the cord selectors CS have access only to operators cords of certain positions, while other cord selectors have access to cords of other positions. In order to preve t he seizure of a cord selector for use which does not have access to cord circuits of the operators position which has been selected by the finder switch OPF, the relay 532 is provided, which, as hereinbefore described, was energized in positions 3 and 4 of the sequence switch 500. This relay upon energization placed a ground potential upon the bank contact 540 of each set of bank terminals connected to cord selectors not having access to the cords of the operators position selected. Assuming that the finder selectorswitch FS had been moved to such a set of terminals leading to an idle cord selector, the selector FS would not have been arrested with its brushes thereon, as hereinbefore described, since the energization of relay 534 would still have been maintained over a circuit extending from grounded battery through the right-hand winding of relay 534, through the lower right-hand contact of sequence switch spring 513 (3 to 9), through the upper left-hand contact of sequence switch spring 513 (3 and 4), through brush 541, bank contact 540, and thence to ground through the front contact and armature of relay 532. The switch FS would, therefore, continue hunting until an idle cord finder was found which has access to the cords of the selected operators position.

Reverting now to that point in the establishment of the connection when relay 534 deenergized, a circuitwas closed at the righthand armature and back contact of said relay, which extends through the lower contact of sequence switch spring 516 for moving the sequence switch 500 out of position 4 and through the co5peration of the master contact 501 into position 8. At its left-hand armature and back contact, relay 534 also closes a circuit for extending a busy ground potential to the test terminal of the set of bank contacts upon which the brushes of switch FS are now resting, which extends from ground at the lower left-hand contact of sequence switch spring 512 (4 and 5), through the back contact and left-hand armature of relay 534, through the lower lefthand contact of sequence switch spring 515 (3 to 5), and thence through the test brush 536 to the test terminal of the bank. As soon as the sequence switch 500 leaves position 5, this circuit is interrupted, but a new busy potential circuit is closed directly from the test brush 536, through the lower left-hand contact of sequence switch spring 509 (5 to 14), through the inner armature and front contact of relay 528 and thence to ground at the upper armature and front contact of relay 522.

"When the sequence switch 500 reaches position 3, a circuit is closed from grounded battery through resistance 535, through the contact of sequence switch spring 517 (8 to 11), over wiper 542 of the switch SLF and the bank terminal upon which it is-resting,

through the wiper 412 of the primary line finder PLF and the bank terminal upon which it is resting, to the multiple bank test terminals 114 of the calling line, thereby placing a selectable'calling potential upon the test terminals of the callingline appearing before all ofthe line finders which have access thereto. A circuit is also closed for the group brush trip magnet 115 corresponding to the group in which the calling line is located, which circuit extends from grounded battery through the magnet 115, through the bank contact 543 and wiper 544 resting thereon, and thence to ground at the lower right-hand contact of sequence switch spring 508 (8 to 10).

In position 8 of sequence switch 500 a circuit is also closed for the start relay 116 (Fig. 1) which extends from grounded battery through resistance 117, lower contact of sequence switch spring 104, through the winding of relay 116, through the lower contacts of sequence switch spring 105, over one limb of the talking circuit, shown in heavy lines, through the brush 545 of the switch FS, through the upper contact of se quence switch spring 516 and through the back contact and right-hand armature of relay 534 to ground. Relay 116 upon energizing causes the energization of sequence switch magnet 100 to drive the sequence switch out of position 1 and into position 2, this circuit extending from grounded battery through magnet winding of the sequence switch, through the upper contact of sequence switch spring 106 to ground at the left-hand armature and front contact of relay 116. In positions 2 to 18, inclusive, the sequence switch 100 connects busy ground potential from the lower right-h and contact of sequence switch spring 102 (2 to 18), to the test terminals individual to the paired line finder and cord selector switches multiplied. into the banks of all finder selector switches FS having access thereto, to prevent seizure Of these paired switches by other finder selectors.

The circuits of the system are now in. condition for the operation of the line finder switch LF for hunting for the terminals of the calling line. This function is, however, dependent upon the condition of the finder allotter switch FA, which, at this time, determines the precedence of calls. If there is no other calling subscriber of the same group entitled at this time to a connection, the sequence switches 500 associated with all other selector finders FS of the group will be either in positions 1 to 4 or 11 to 18, and consequently upon the movement of sequence switch 500 associated with the circuits shown in Fig. 5, a circuit is established for the relay 524 which extends from grounded battery through the stepping magnet 523 and its interrupter contacts,through the relay 524, through the lower contact of sequence switch spring 518 (8), through the upper contacts of sequence switch springs 518 (11 to 4) of other sequence switches 500, to ground through the bank contact and wiper 546 of allotter FA. Relay 524 thereupon energizes, but owing to its resistance stepping magnet 523 does not energize. Relay 524 upon energizing closes a circuit for causing the movement of sequence switch 500 from position 8 into position 9, this circuit extending from grounded battery through the winding of sequence switch magnet 500, through the lower left-hand contact of sequence switch spring 507 to ground at the left-hand armature and front contact of relay 524. At its right-hand armature and front contact, relay 524 closes a locking circuit for itself which may be traced from grounded battery at the stepping magnet 523, through the winding of relay 524, through the upper contact of sequence switch spring 506 (8 to 16), through the right-hand armature and front contact of relay 524, through the upper right-hand contact of sequence switch spring 504 (8 to 11), through the brush'547 of the switch FS and the bank contact upon which it is then resting, through the left-hand contacts of sequence switch spring 107 (2 to 4) and (2 and 3), through the conducting portion of segment 118 of the commutator 7 of the line finder LF (Fig. 1), and thence to ground through, the shaft wiper 119. Upon leaving position 8 the initial energizing circuit through relay 524 is broken at sequence switch spring 518.

In position '9 of the sequence switch a circuit is closed for relay 534 which may be tracedfrom grounded battery through the right-hand winding of relay 534, and thence to ground at the lower contacts of sequence switch spring 513 (3 to 9) and Belay 534 is energized in this circuit and at its right-hand armature and front contact closes a circuit for driving the sequence switch 100 (Fig. 1) out of position 2 and into position 3. This circuit extends from grounded battery through the magnet winding of sequence switch 100, through. the lower left-hand contact of sequence switch spring 103 (2), through the bank contact 548 and the brush 549 of switch FS resting thereon,through the upper right-hand contact of sequence switch spring 514 (8 to 11) to ground at the right-hand armature and front contact of relay 534. A circuit is also closed at the right-hand armature of relay 534 for causing the energization of the se-v quence switch magnet of sequence switch 500, which thereupon is driven out of position 9 and into position 10. This circuit extends from grounded battery through the winding of the magnet of sequence switch 500, through the lower contact of sequence.

switch spring 514 (9) to ground at the right-hand armatur and front contact of relay 534. Upon leaving position 9 the initial energizing circuit is broken at the lower contact of sequence switch spring 518, but the relay is maintained energized through positions 2 and 3 of sequence switch 100 over a circuit extending from grounded battery through resistance 535, through the left-hand winding of relay 534, through its left-hand armature and front contact, through the lower right-hand contact of sequence switch spring 515 (8 to 11), through the brush 550 of the selector finder FS and the bank terminal upon which it is resting, through the lower left-hand contact of sequence switch spring 108 (2 l and 3), through the upper contacts of sequence svitch spring 105 (2 and to ground. The ing circuit of start relay 522 is broken as soon as sequence switch 500 leaves position 9 at the upper contact of sequence switch spring 502, and relay 522 thereupon deenergizes.

Operation of main Zinc finder.

In position 3 of sequence switch 100 a.

circuit is established for the updrive magnet of line finder Li This circuit may be traced from grounded battery through the winding of the updrive magnet 120, through the lower contacts of sequence switch spring 109 and to 12), through the bank contact 548 and brush 549 of finder selector switch FS, through the upper right-hand contact of sequence switch spring 514 (8 to 11), and to ground at the front contact and right-hand armature of relay 534. The updrive magnet 120 energizes, thereby forcing the depending extension of the shaft 1 of switch LF against the constantly rotating roller 3. The brush sets 2 of the switch are thereupon. moved upwardly. Upon the upward movement of the switch shaft the set of brushes having access to the group of lines in which the calling line is located is tripped by a trip finger 6 on the trip rod 5. The finger 6 having been rotated into position by the energized trip magnet 115, all in the well-known manner. Continued movement of the switch shaft 1 traverses the tripped set of brushes over the bank of contacts to which they have access.

As soon as shaft wiper 119 moves oil of the conducting ortion of segment 118 of the commutator the holding circuit of relay 524 is broken and relay becomes deenergized closing at its lefthand armature and back contact a circuit through the lower right-hand contact of sequence switch spring 507 (10) for driving the sequence switch into position 11, and closes at its right-hand armature and back contact a holding circuit through the ri ht-hand winding of reholdlay 534, which may be traced from grounded battery through the right-hand winding of relay 534, through the upper contact of sequence switch spring 503 (10 and 11), through the back contact and right-hand armature of relay 524, through the upper righthand contact of sequence switch spring 504 (8 to 11), through brush 547 of switch FS, through the left-hand contacts of sequence switch spring107 (2 to 4) and (2 and. 3), to commutator segment 118 and ground at shaft w'per 119 during the en gagement of the wiper 119 with the conducting portion of the commutator.

Upon the engagement of the switch brushes with the multiple terminals of the callingline, a shunt circuit is closed around the lefthand holding winding of relay 534 which extends from one terminal of the winding through the contact of sequence switch 517 (8 to 11), through the wiper 542 of switch .SLF, through the wiper 412 of switch PLF, through the test terminal 114 of the calling line, through the test brush 121 of the line finder LF, through the lower left-hand contact of sequence switch spring 108 (2and 3), through the brush 550 of finder selector FS, through the lower righthand contact of sequence switch spring 515 8 to 11), and thence to the other terminal of the winding of relay 534, through the left-hand armature and front contact there of. The establishment of this shunt circuit about the winding of relay 534 causes the flow of current through the left-hand winding to cease, but relay 534 is still held energized over the circuit previously traced through its right-hand winding until the brushes of switch LF are properly centered on the terminals of the calling line, when shaft wiper 119 will no longer engage the conducting portion of the commutator segment 118, and the circuit through the righthand winding of relay 534 will, therefore,

be opened. Relay 534 now deenergizesand at'its right-hand armature and front contact opens the previously traced circuit of the updrive magnet 120. The switch shaft of finder LF thereupon comes to rest.

hen relay 534 deenergizes a circuit is closed for energizing the magnet of the sequence switch 100 which may be traced from grounded battery through the magnet winding of sequence switch 100, through the lower contacts of sequence switch spring 110 and to 12), through the brush 545 offinder selector FS, through the upper contact of sequence switch spring 516 11), and thence to ground at the right-hand armature and back contact of relay 534.

Upon its. energization the sequence switch 100 moves out of position 3 and comes to rest at position 4. In position 4 of sequence switclrlOO a busy potential is placed upon the test contact 124 of the Calling line for secondary, finder switch.

holding the cut-off relay 9 energized, which circuit may be traced from grounded battery through resistance 125 over the upper contacts of sequence switch spring 111 and throughbrush 126 of theline tinder LF.

At the time the line finder LF was testing for the multiple contacts of the calling line, had there been another line in the same subgroup upon whose multiple test terminal 114- a calling potential existed, the line find er LF would not have been arrested with its brushes upon the terminals of such line as no shunt circuit would have been connected around the winding of relay 53% upon the engagement of the test brush 121 of the line finder with the test terminal 11 of such line; Thus, the only finder switch that is enabled toconiiect with a particular calling line is the finder switch which has been *startedthrough circuits established by the seizure of that calling line by a primary and Sequence switch 500 upon leaying position 10 opens the circuit of too line finder trip magnet 115 at the lower right-hand contact of sequence switch spring 508. V1011 sequence switch 500 in position 11 a circuit is closed for advancing finder allotter switch FA one step, which circuit may be traced from battery through the winding of stepping magnet 560 and thence to ground at theupper contacts of sequence switch spring 519. In position 11 a circuit is also closed for driving the sequence switch 500 out of position 11 and into position 14; This cir-.

cuit may be traced from grounded battery through the. magnet winding of sequence switch 500 through the-upper left-hand contact of sequence switch spring 507 (11), through the lei'thand armature and back contact of relay 534, through the lower right-hand contact of sequence switch spring (8 to 11), through brush 550 and the bank contact upon which it is resting,

through the upper left-hand contact of se' quence switch spring 108 (4 and and thence to ground at the normal contact of 122 of the'coznmutator 7 of cord selector C-Sand the grounded shaftwiper 123. The

and the operators head set 0 over a circuit which may be traced through the heavy line conductors from grounded battery through the lower right hand winding of the operators repeating coil 201, through the windin of relay 203, over the bank contact 551 an 7 the 1 ,seam'r A, through the brush 127, through the upper left-hand and lower right-hand contacts of sequence switch spring 109, through brush 5&9 of switch FS, through the lower contacts of sequence switch spring 511 (12 to 16), through the wiper 531 of switch ()PF, and thence to ground through the upper righthand'winding of repeating coil 201. "R8 lay 203 is energized over this circuit and closes a circuit for the slow acting relay 600 of the. class of service register individual to the selected'operatofis position. This circuit may be traced from grounded battery through the winding of relay 600 to ground at the armature and front'coiitact ot' relay 203. Relay 600 upon being energized closes a new locking circuit for relay 528 extending from ground at'its left-hand armature, through wiper 5290f switch OPRthrough the lower right-hand contact ofsequence switch spring .509 (1' to 16), through armature and front contact of relay 528 and to groundedbattery at the winding of stepping magnet 527, and establishes a circuit for relay 601 over the No. 1 pick-up conductor a; to thecom niutator disk 413 of the class of service interruptei', shown in Fig. 4. This circuit may be traced from grounded battery through the winding of relay 601, through the right-hand armature and front contact of relay 600, over the conductor a, through the brush inengageiiieiit with the disk 4:13, and to ground at commutator disk 4:14. As soon as the disk 4:13 has been rotated into the proper position by its constantly rotatingdi'iving shaft, this circuit is completed and relay 601 becomes energized. The transmission of the pick-up iiiipulse over conductor a immediatelyprecedes the rotation of disks 4:15, 418 and 419 into positions effective tor the transmission of class of service impulses and insures that no impulses will be effective until the disks are in a particular rotary position. A circuit is now closed for relay 602 extending from grounded battery through the winding of relay 602, through the back contact and left-hand armature of relay 603, and thence to ground at the front contact and armature of relay 601. Relay 602 is energized; and locks itself up over a' circuit extending through its right-hand armature and front 0011ia0i3,tl1r011gh the wind-' opens the initial energizing circuit of re lay .602. 7

Upon the energization of relay 602 a circuit is closed, over which class of service in dicating impulses may be sent for setting up the class of service register at the operators position. Assuming that the calling subscriber is located in a private branch exchange and is entitled only to limited service, two series of class of service impulses will be sent to the operators register. The first series of impulses will be sent from the commutator disk 115 for setting up section C of the class of service register over a circuit extending from grounded battery at the class of service interrupter, Fig. 4, through commutator disk e15, through the lowermost terminal of the bank of switch PLF, tl'irough wiper 116 resting thereon, through the middle terminal of switch SLF and wiper 553 resting thereon, through the lower belt-hand and upper right-hand contacts of sequence switch spring 520 (3 to 16), through wiper 55-1 of switch OPF and the bank terminal upon which it is standing, through the front contact and left-hand armature of relay 609, through the winding of relay 605, and thence to ground at the outer left-hand contact of relay 604. Relay 605 in response to the first impulse over this circuit closes a circuit for the relay 606 of section C of the register, which may be traced from grounded battery through the Winding of relay 606, through the back contact and inner right-hand armature of relay 609, through the back contact and righthand armature of. relay (311, through the back contact and right-hand armature of relay 610, through the back contact and outer right-hand armature of relay 609, through the back contact andv left-hand armature of relay 612, and thence to ground at the front contact and armature of relay 605. Relay 606 upon energizing closes a locking circuit for itself extending through its winding and its right-hand armature and front contact, through the winding of relay 609, through the back contact and lef hand armature of; relay 610 and thence to ground at the front contact and armature of relay 600. Relay 609 is energized in this circuit and at its armaturcs and back contacts opens the initial energizing circuit of relay 606, and its outer armature and front contact prepares a circuit for the relay 607. Upon the next response of relay 605 to a second impulse from the class of service interrupter, the relay 60? is energized over a circuit extending from grounded battery through the winding of relay 607, through the outer right-hand armature and front contact of relay 609, and thence to ground at the armature and front contact of relay 605 over the circuit previously traced. Relay 607 closes a locking circuit for itself extending through its winding-and righthand armature contacts, through the wind ing of relay 610, through the hack contact and left-hand armature of relay 611, and thence to ground at the front contact and left-hand armature of relay 600. Relay 610 Is now energized and at its left-hand arma ture and back contact opens the looking circuit of relay 606, which, together with relay (509, deenergized. Relay 609 upon deenergizing opens the initial energizing circuit of relay 607, and at its right-hand armature and back contact prepares a circuit for the relay 608. In response to the third energization of relay 605, a circuit is closed for relay 608 extending from grounded battery through the winding of relay 608, through the right-hand armature and front contact of relay 610, through the back contact and outer right-hand armature of relay (309 to ground through the armature and front contact of relay 605 over the circuit previously traced. Relay 608 is energized orer this circuit and locks up over a circuit extending through its right-hand arn1ature and front contact, through the winding of relay 611, and thence to ground at the left-hand armature and front contact of relay 600. Upon energizing relay 611 at its left-hand armature and back contactopens the rocking circuit through relays 610 and (307, which thereupon become de'e'nergized. It is,therefore, apparent from the forego ing that only one pair of register relays, namely, the pair last energized will remain in an energized condition Following the class of service impulses of the first series which determine the line characteristics of the calling line, an impulse is transmitted over the No. 2 pick-up conductor Z) for causing the 'energization of relay 612. This impulse of current flows over a circuit extending from grounded loattery through the normally closed right-hand armature contacts of relay 612, through the right-hand armature and front contact of relay 603, over the No. 2 pick-up conductor Z), through. the No. 2 pick-up commutator disk 417, and to ground at the disk 414. Relay'612 is energized and at its right-hand armature closes a locking circuit for itself and opens its initial energizing circuit, the locking circuit extending to ground at the left-hand armature and front contact of relay 600. At its inner left-hand armature and front contact, relay 612-closes a circuit for the class of service lamp relay 613, which may be traced. from grounded battery through the winding of relay 613, through thefront contact and left-hand armature of relay 608, and thence to ground at the inner left-hand armature and front contact of re lay 612. Relay 613 upon energizing closes at its upper armature and front contact a circuit for the indicating lamp 313, which,

in the case assumed, indicates to the operator that the calling subscriber is located at a private branch exchange, and the relay at its other armature contacts prepares circuits which will be hereinafter described.

Following the termination of the impulse over the No. 2 pick-up conductona second series of impulses is transmitted from the class of service interrupter for setting up the relaysof section D of the class of service register in substantially the same manner as hereinbefore set forth in connection with the setting of section C. Briefly, the impulses of the second series causes the energization and deenergiaation of relay 605 since relay 602 is now energized which retransmits the impulses from its grounded armature con tact through the outer left-hand armature and front contact of relay 612 to relays G14, G15 and 616 in succession. there are three impulses in the series for the purpose of indicating that the ca-llingsubscribers line is provided with a coin box, relay 616 energizes upon the reception of the last impulse of the series and'locks up over acircuit extending from grounded battery through its winding and its right-hand armature and front contact through the winding ofrelay 617, and thence to ground at the front contact and left-hand armature of relay 600. Following the termination of r the second series of impulses, relay 601 again energizes by an impulse over the No. 1 pickup conductor and at its armature and front contact closes a circuit for relay (30st which circuit may be traced from grounded battery through the winding of relay 60 1,

through the normally closed right-hand outer left-hand armature and back contact opens the circuit through relay 605 to prevent the further oper tion of relay 605 in response to further impulses from the class of service interrupter, at its outer left-hand armature and front contact prepares a circuit for subsequently driving sequence switch 300 at the operators position outof position 8, and at its inner left-hand arniature and front contact closes a circuit forthe class of service lamp relay (318. The circuit for relay 618 may be traced from grounded battery through the winding of the relay, through the lefthand armature and front contact of relay 616, and thence to ground at the inner left-hand armature and front contact of relay 604. Relay 618 upon energizing closes acircuit at its upper armature Assuming that and front contact for the class of service lamp 314; and at its other armature contacts Selection of'cord circuit at ope'mtors posetz'o'n.

The operator has now been warned that a calling line is about to be connected to one of her cord circuits and through the'class of service lamps is appraised of the nature of the calling line and the class of service to which such line is entitled. During the setting of the operators service indicating register sequence switch 500 has been moved in thefunctioning of the 'alloter SA, or if upon reaching position 1% there was no other call entitled to precedence, such sequence switch has proceeded into position 15. Under the assumption that no other cord sc lector is entitled to precedence of connection Vwith the selected operators position, upon reaching position let, a circuit is closed for relay 52 1 which may be traced from grounded battery through the winding of stepping magnet 523, through the armature contacts of magnet 5235'through the winding of relay through the lower contact of sequence switch spring 521, through the upper contacts of sequence switch springs 521 (6 to 11) of other sequence switcheshtlth to ground at the bank contact and wiper of the alloter SA. Relay 524 is energizedand at its right-hand armature-and front contact closes a locking circuit through its winding extending from grounded battery through the winding of stepping magnet through the winding of relay 5%, tlirough the upper contact of sequence switch spring 506(8 to 16) through the front contact andi'ight-hand armature of relay 5%, through the upper left-hand contact "of sequence switch spring 50a (lei-to 15), through brush 550 of tinder selector FS and the bank contact upon which it is resting. through the upper leftdiand contact of sequence switch spring 108 i and 5), and thence to ground at the normal segment 122 and'shaft wiper 123 of the commutator 7 of switch US. At itsleft-hand armature and front contact a circuit is closed from ground through the lower left-hand contact of sequence switch spring 507 (14:)

for driving the sequence switch 500 out of position 14 and into position 15., In position 15 a circuit is closed from ground over the upper contacts oi ,seque1ice switch spring 505 for the stepping magnet 557 of the allotter SA. which moves its bush to the next contact of its bank. 7

With sequence switch 500 in position 15 and sequence switch 100 in position i, a Cir.- cuit is now closed for the start relay 116 of the cord selector switch CS, which circuit may be traced from grounded battery through resistance 117 through the lower contact of sequence switch spring 10 1, through the winding of start relay 116, through the lower contacts of sequence switch spring 107 (1 and and (2 to 4), through the brush 54:7 of switch FS, through the upper left-hand contact of sequence switch spring 509 (15 and '16), through the lower right-hand contact of sequence switch spring 509 (1 to 16), through wiper 529 of the switch OPF, and the bank terminal upon which it is standing, and thence to ground at the front contact and left-hand armature of relay 600. Relay 116 upon energizing closes a circuit from ground at its left-hand armature and front contact, through the upper contact of sequence switch spring 106 (4) for driving the sequence switch 100 into position 5. In position 5 a circuit is closed for the updrive magnet 129 of the cord selector CS which extends from grounded battery through the winding of the magnet 129, through the lower contact of sequence switch spring 106 (5), and thence to ground at the left-hand armature and front contact of relay 116. Upon the energization of the updrive magnet 116, the depending extension of the switch shaft 1 is pressed into contact with the constantly rotating roller 3, thereby causing an upward movement of the switch shaft. The initial upward movement of the switch shaft carries the brush sets 2 of the switch past their respective tripping spindles 5, and since the tripping magnet 130 corresponding to the group of cords at the selected operators position is at this time energized over a circuit extending through the wiper 556 of the operators position finder switch OPF to ground at the upper right-hand contact of sequence switch spring 512 (14 and 15), the brush set 2 which has access to the cords of the selected position is tripped. Upon further upward movement 01 the switch shaft the tripped set of brushes is traversed over the terminals of its corresponding bank and, so long as the test brush 131 encounters a busy ground potential upon the test terminals ofthe bank, the relay 116, whose initial energizing circuit was opened when sequence switch 100 left position 4, continues to re main energized over a locking circuit extending from grounded battery through resistance 117, through the lower contact of sequence switch spring 104 (1 to 5), through the winding of relay 116, through the righthand contacts of sequence switch spring 107, through the right-hand armature and front contact of relay 116, through the lower left hand contact of sequence switch spring 112, through the test brush 131. When the terminal of an idle cord is found, relay 116 is no longer held energized over the test brush 131 and. becomes deenergized. It does not, however, release its armatures until after the switch wipers have become centered on the bank terminals of the selected cord as lts winding receives current over the circuit, above traced, through the lower left-hand cont-act of sequence switch spring 112, and from thence through the upper left-hand contact of sequence switch spring 112 (4 and 5), through the segment 132 of the commutator 7 of the cord selector, and to ground through the shaft wiper 133. When the switch brushes are properly centered the shaft wiper 133 is in engagement with an insulating portion of the segment 132 and the holding circuit of relay 116 is definitely broken.

Relay 116 upon definergizing connects a busy ground potential upon the test terminal of the selected cord circuit over a circuit extending from ground through the up per right-hand contact of sequence switch spring 113 and 6), through the righti hand armature and back contact of relay 116, and thence through the lower left-hand contact of sequence switch spring 112 (41 to 6) to brush 1341. At its left-hand armature and front contact relay 116 breaks the circuit of the updrive magnet 129, and at its back contact closes a circuit extending through the lower right-hand contact of sequence switch spring 103 (5) for driving sequence switch 100 out of position and under the influence of its master contact 101 into position 12. In position 1.2 a talking circuit is closed from the calling subscribers line, through the brushes of the line finder LF over the heavy conductors, through the up per contacts of sequence switch springs 109 and 110, through brushes of switch CS, and to the strands of the selected cord circuit.

When the switch CS moved from its nor mal position, the holding circuit of relay 521 was broken at the normal commutator segment 122 and relay 521 thereupon'became deenergized closing at its left-hand armature and back contact acircuit through the lower right-hand contact of sequence switch spring 507 (15) for driving sequence switch 500 into position 16. In position 16 a circuit is closed for driving the sequence switch 100 out of position 12 and into position 1 1. This circuit may be traced from grounded battery through the magnet winding of ,se quence switch 100, throughithe upper righthand contact of sequence switch spring 108 (12), through the switch brush 550,,and thence to ground through the upper rig-h hand and lower left-hand contacts of sequence switch spring 513 (16). Upon leaving position 12 sequence switch 100 opens a circuit which has held relay 203 at the operators position energized, whereupon re lay 203 deenergizes and opens the circuit of the slow-acting holding relay 600, which, after an interval, disconnects ground at its left-hand armature and back contact from the holding circuits of relays 602, 603', 604.

' The deenergization of relays 608 and 616' causesthe deenergization of the lamp relays service register are now restored to 608, 611, (312, 616 and 617 ot the selected class of service register which thereupon be come deenergized. Belay 600 also opens the circuit extending through wiper 529 of switch OFF which has held the relay 52S Relay 528 deenerglzes closing energized. at its outer right-hand armature and back contact a circuitfor driving sequence switch 500 out of position 10 and into position 18.

This, circuit may be traced from grounded" battery through the magnet winding of sequence switch 500, through the right-hand contact of sequence switch 7 spring 510 (3 to 16), and thence to ground at the hack contact and armature of relay 528.

at the contacts of sequence switch spring.

508 (2 to 12). Relay 409 thereuponbecame deenergized opening the holding circuit of. relay 03. All the circuits of the primary finder switch are now in normal condition. Busy ground potential is also removed from the test wiper 525, thereby rendering the bank terminals leading to the primary finder switch selectable by other secondary finder switches. In position 18 of sequence switch '500 a circuit is closed for the downdrive magnet 558 of the finder selector switch FS, which extends from grounded battery through the windnig of the downdrive magnet 558, and thence to ground through the upper left-hand and lower right-hand contacts of sequence switch spring 520 (18).

. presses the depending extension of the switch shaft against the constantly r0 tating downdrive. roller d, therebycausmg the restoratlon of the switch shaft and brushes to normal. When the shaft wiper 539 engages the normal segment 559 of the commutator 7, a circuit is closed for driving sequence switch 500 out or". position 18 and into normal. position. This circuit'may be traced from grounded battery throughthe magnet winding of sequence switch 500,through the upper righthand contact of sequence switch spring 507,

and thence to ground through the normal contact 559 and shaft wiper 539. All ofthe circuits of the finder selector are now in normal condition.

Returning new to the point in the establishment. of the connection when sequence switch 100 was driven out of position 5 and The magnet 558 upon energizing into position 12, when sequence. switch 100 reached position-6, a circuit was closed over the lower right-hand contact of; sequence swltch spring 112 for placing a busy potential at the multiple test contacts of theselected cord circuit, and a circuit for energizing the relay 3150f the selected cord circuit. This circuit may be traced from grounded battery through the winding or relay 315, through the lower contact of the sequence switch spring 302 (1), through normally closed c911 tacts of the operators charge key K, through brush 13d of switch CS, and thence to ground at the upper right-hand contact of sequence switch spring 102 ('0 to 10). Re

lay 315 is energized over this circuit and locks up over a circuit extending through its winding and right-hand armature and trout contact to ground at the upper contactoi sequence switch spring 303 (lto a).

At its left-hand armature and front contact, relay 315 closes a circuit extending through the upper right-hand contact of sequence switch spring 30-3: (1) for driving sequence switch 300 into position 2. In position 2 sequence switch 300 closes a circuit for the answering sleeve relay 20st, which extends from grounded battery through the winding of relay 204;, through the back contact and outer left-hand armature of relay 316, through the upper contact of sequence switch spring 302 (2 to 18), through the normallly closed contacts of charging key K, and to ground at sequence switch spring 102 over the circuit previously tracedj 1 0 Relay 204 is ener ized over this circuit and at its outer right-hand armature and front contact connects a ground potential. to the multiple test terminals 135 of the selected cord circuit in the banks oi all cord 5.

selectors having access to such cord circuit to prevent seizure of the cord circuitby another cord selector. At its left-hand armature and front contact, relay 20 lcloses a circuit for the supervisory lamp 205,.extenchng 11 from grounding battery through the lamp 205, through the lett-hand armature and front contact of relay 204C, and thence to ground at the armature and back contact of v the answering supervisory relay 206. A cir- 11 cuit is also closed at this time, provided the operator is at her position, for the common listening I relay 207, which extends from grounded battery through the relay 207,

through the inner right-hand armature and front conttuitoi relay 204. through sequence switch contact 305' (2), through tlienormally closed contacts of the listeningin keys K, individual to the several cords of the operators position, through the winding of the common listening-out relay 200. and thence to ground at the key contacts 208 oithe opcrators head set. Relays 2002\nd. 20? ener' Q1710 over this circuit, relay 200 connecting round iotential over its armature and front 13.0 23

calling sleeve 95 

